The present invention relates to a refractory discharge device for use in discharging molten metal, particularly molten steel, from a metallurgical vessel and which during use is immersed in the discharged molten metal. More particularly, the present invention relates to such a refractory discharge device including a refractory immersion nozzle that has attached to an outer surface thereof a separate refractory member that, during use of the refractory discharge device, extends above and below a casting powder covering or layer of the molten metal into which the refractory discharge device will be immersed. This separate and attached refractory member thus operates as an external reinforcement that is resistant to stresses created by the casting powder covering or layer.
A refractory discharge device is disclosed in German DE-PS 20 42 897. This device includes an external reinforcement that is attached to an immersion nozzle by means of threading, a bayonet lock or stops. The immersion nozzle and the external reinforcement member are made of the same refractory material.
In German DE-AS 29 36 480 there is disclosed an immersion nozzle having a refractory layer integrated into the material thereof at a region that is to be at the level of the upper surface of the molten metal. This layer is to contain, inter alia, 70 to 90 % zirconium oxide and 2 to 10 % carbon. This layer is fabricated as one piece with the immersion nozzle, and in practice this requirement causes difficulties. The carbon content of this layer is a drawback since it can burn out during use of the device. This creates an increase of porosity of the layer and thereby makes such layer susceptible to erosion. Another disadvantage is due to the fact that mechanical stresses that necessitate preparation for spalling of the layer under temperature stresses are generated due to the layer and the immersion nozzle being formed as one single integral member. Also, the refractory material of the immersion nozzle contains aluminum oxide and carbon. Carbon contributes to the bonding of the aluminum oxide during formation of the immersion nozzle and also provides advantageous thermal conductivity of the immersion nozzle. Thus, the immersion nozzle is erosion resistant with respect to the molten metal itself, particularly molten steel.
In German DE 33 41 524 C3 a refractory molded member made of partially stabilized zirconium dioxide is disclosed. This member is formed without carbon, and CaO, MgO or Y.sub.2 O.sub.3 is provided for stabilization. This member is bonded directly without carbon and binder by burning at high temperatures ranging from 1600.degree. to 2000.degree. C.